Commit 2101c878 authored by Uwe Kleine-König's avatar Uwe Kleine-König Committed by Thierry Reding
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pwm: atmel: Replace loop in prescale calculation by ad-hoc calculation 



The calculated values are the same with the modified algorithm. The only
difference is that the calculation is a bit more efficient.

Acked-by: default avatarClaudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: default avatarUwe Kleine-König <uwe@kleine-koenig.org>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent ff55e7a3

drivers/pwm/pwm-atmel.c

+17 −7
Original line number Diff line number Diff line
@@ -60,7 +60,7 @@ struct atmel_pwm_registers { 
};



struct atmel_pwm_config {

	u32 max_period;

	u32 period_bits;

};



struct atmel_pwm_data {
@@ -119,17 +119,27 @@ static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip, 
{

	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);

	unsigned long long cycles = state->period;

	int shift;



	/* Calculate the period cycles and prescale value */

	cycles *= clk_get_rate(atmel_pwm->clk);

	do_div(cycles, NSEC_PER_SEC);



	for (*pres = 0; cycles > atmel_pwm->data->cfg.max_period; cycles >>= 1)

		(*pres)++;

	/*

	 * The register for the period length is cfg.period_bits bits wide.

	 * So for each bit the number of clock cycles is wider divide the input

	 * clock frequency by two using pres and shift cprd accordingly.

	 */

	shift = fls(cycles) - atmel_pwm->data->cfg.period_bits;



	if (*pres > PWM_MAX_PRES) {

	if (shift > PWM_MAX_PRES) {

		dev_err(chip->dev, "pres exceeds the maximum value\n");

		return -EINVAL;

	} else if (shift > 0) {

		*pres = shift;

		cycles >>= *pres;

	} else {

		*pres = 0;

	}



	*cprd = cycles;
@@ -289,7 +299,7 @@ static const struct atmel_pwm_data atmel_sam9rl_pwm_data = { 
	},

	.cfg = {

		/* 16 bits to keep period and duty. */

		.max_period	= 0xffff,

		.period_bits	= 16,

	},

};
@@ -302,7 +312,7 @@ static const struct atmel_pwm_data atmel_sama5_pwm_data = { 
	},

	.cfg = {

		/* 16 bits to keep period and duty. */

		.max_period	= 0xffff,

		.period_bits	= 16,

	},

};
@@ -315,7 +325,7 @@ static const struct atmel_pwm_data mchp_sam9x60_pwm_data = { 
	},

	.cfg = {

		/* 32 bits to keep period and duty. */

		.max_period	= 0xffffffff,

		.period_bits	= 32,

	},

};